The precise signaling pathways that mediate the transforming and oncogenic action of mutated Ras proteins remain to be defined. First, although Ras interaction with the Raf serine/threonine kinases is clearly important for Ras transformation, how Ras promotes Raf activation remains complex and unresolved. Second, recent studies clearly demonstrate that both Raf-dependent and Raf- independent effector pathways are essential to promote full Ras transformation. For example, a Raf-independent pathway involving Rho family proteins has been shown to be important for Ras activation of the Jun N-terminal kinase (JNK) pathway. However, the effector that connects Ras with Rho remains to be elucidated. This proposal describes three specific aims to further delineate the downstream interaCtions and signaling pathways that mediate Ras oncogenicity. First, we recently showed that the interaction between Ras and Raf is more complex than originally thought. Instead of a simple binding of the switch I domain of Ras to an N- terminal Ras binding domain in Raf, a second interaction between the Ras switch II domain and the Raf cysteine-rich domain (Raf-Cys) also occurs. We have also defined a putative consensus Ras-binding sequence in Raf-Cys and in other candidate Ras effectors (e.g., Ra1GDS). This second interaction appears to be critical for Ras activation of Raf and for Ras transformation. Experiments are proposed to establish the role of Raf-Cys in Ras activation of Raf. Whether RalGDS interacts with Ras switch I and II will also be addressed. Second, we recently showed that pl 20 Ras GAP may specifically modulate a Raf-independent signaling pathway leading to JNK. Experiments will be performed to determine if pl 20 Ras GAP serves as the link between Ras and the Rho family proteins, to cause activation of JNK and serum response factor. Finally, we will determine if the Rho family member Rac1 activates its effectors by interactions with switch I and II, and with other C-terminal sequences. The identification of key components that mediate Ras transformation may identify important targets for the design and development of novel cancer chemotherapeutic approaches.